CN100380419C - display screen - Google Patents

Abstract

A display device includes a control circuit (50) for changing the time period of the signal voltage applied to each signal line (42-1 to 42-n) and the scanning voltage applied to each scanning line (41-1 to 41-m) within a vertical scanning period (T). The control circuit (50) controls each horizontal scanning period (t1 to tm) in such a manner that the period gradually increases from the scanning line (41-m) close to the vertical driving circuit (30) to the scanning line ( _41-1 ) far from the vertical driving circuit ( ₃₀ ). In this way, when writing a signal voltage to a pixel via the signal line, a target potential is reached at each pixel within the time period of applying the signal voltage.

Description

display screen

Background of the invention

The invention relates to a display device comprising:

a matrix of pixel rows and columns,

a set of first conductive lines, each first conductive line coupled to each pixel row,

a set of second conductive lines, each second conductive line coupled to each pixel column,

first voltage applying means for sequentially applying a scanning voltage to each of the first conducting wires and a first voltage applying means for respectively applying respective signal voltages to each of the second conducting wires in synchronization with the scanning voltage sequentially applied to the first conducting wires Two voltage application devices.

In recent years, electronic equipment equipped with a flat panel display such as a liquid crystal display (hereinafter referred to as "LCD"), a plasma display (PDP), a field emission display (FED) and an organic EL (electroluminescence) display as a display device is gaining popularity. widely used. First, the widespread use of electronic devices equipped with LCDs is remarkable and their application coverage is quite wide.

Examples of LCDs include so-called active matrix type LCDs using thin film transistors hereinafter referred to as "TFT". These TFTs make it possible to configure LCDs with multiple scan lines (as required for large-screen or high-definition displays), with excellent display properties such as contrast ratio and switching response. Such active-matrix LCDs typically contain an array of pixels arranged in a matrix of horizontal and vertical lines. Horizontal lines are also called scan lines or rows; vertical lines are also called signal lines or columns. Driver circuits are provided for both horizontal and vertical lines, and each pixel is equipped with a thin film transistor as a switching element. In this kind of LCD, in order to drive the TFT sequentially row by row, the horizontal drive circuit cyclically supplies sequential scan voltages to the scan lines, while the vertical drive circuit, which operates synchronously with the horizontal drive circuit, selectively supplies voltage to the signal lines according to the image signal. signal voltage. In this method, pixels are selected by scanning lines from top to bottom one row of pixels at a time. The signal voltage is sequentially applied to each corresponding electrode of the pixels on the selected scan line via the corresponding signal line. Signal voltages are written to the corresponding electrodes of the pixels and the image is displayed on the display. Therefore, during a time period in which one scan line is selected, hereinafter referred to as a "horizontal scan period", a signal voltage is supplied to pixels corresponding to the scan line.

However, since the signal lines are generally made of conductive materials, the above-mentioned conventional LCD has a problem that the time constant of the signal lines affects the display performance of the LCD. This tends to become especially severe with large and high-definition displays.

FIG. 4 is a timing chart when voltage is applied to each pixel of a conventional LCD. 4A to 4E illustrate the signals on the scan lines of the first to third rows R1, R2, R3, the (M-1)th row RM-1, and the Mth row RM, and FIG. 4F illustrates a near level denoted NES Signals of any signal line of the driver circuit, FIG. 4G illustrates the signal of a signal line remote from the horizontal driver circuit denoted FES. As shown in FIGS. 4A to 4E, the horizontal scanning period t is a time period allocated to each line for scanning the line. In the vertical scanning period T, the selection of all scanning lines is completed at one time. For this reason, if the time constant increases, as shown in FIG. 4F, although the writing pixel is on the near-end surface NES close to the vertical driving circuit, the signal voltage still reaches the target potential TP within the horizontal scanning period t, For the pixels on the far end surface FES away from the vertical driving circuit, the waveform of the signal voltage applied to the signal line becomes flat and the signal voltage does not reach the target potential TP in the horizontal scanning period t, which makes writing to the pixel correct signal voltage becomes difficult. This causes deterioration of the display performance of the device, such as brightness deviation.

One possible solution to this problem is to lengthen each horizontal scanning period t. However, simply extending each horizontal scanning period t means extending the vertical scanning period T, which leads to deterioration of display quality due to flicker.

Contents of the invention

The purpose of the present invention is to provide a display device, which can write signal voltages without changing the vertical scanning period to make the signal voltages of all pixels reach the required potential compared with the prior art. The invention is defined by the independent claims. The dependent claims define preferred embodiments.

The display device of the present invention is characterized by further comprising a period changing means for changing the time period of applying the signal voltage according to the distance between a row of pixels and the second voltage applying means. It should be noted that a "pixel" in the present invention includes elements associated with the pixel. The terms "row of pixels" and "column of pixels" are used to identify two groups of pixels that are generally substantially perpendicular to each other, so the terms "row" and "column" are interchangeable. In the display device of the present invention, the time period for applying the signal voltage to each pixel on each second wire can be set to any value. Therefore, the display device of the present invention can control the voltage application period in such a way that the time period in which the voltage is applied to each pixel is extended because it is difficult to reach the target potential because the pixel is coupled to the second wire.

The period varying means more particularly selects the time period for applying the signal voltage to be longer when the signal pitch between a row of pixels and the second voltage applying means increases. In addition, the period changing means is effectively controlled so that the time period for applying a voltage to the corresponding pixel on each second wire is gradually extended from the far end face to the near end face of each second wire.

Preferably, the period varying means changes the time period of the scanning voltage applied to each first wire in synchronization with the time period of the signal voltage applied to the pixel through each second wire. In this way, it is possible to easily control the timing of the voltage application of the first and second sets of wires.

Another display device of the present invention is characterized in that it further comprises a period changing means for changing each time period of applying the voltage to each of the first conducting wires within a fixed period during the period when the voltage is applied to all the first conducting wires. This display device of the present invention also allows the period changing means to set each time period for applying a voltage to each first wire to an arbitrary value. Therefore, it is possible to control the voltage application time in such a way that the period of time during which the voltage is applied to the first wires is extended in the region of the group of second wires in which it is difficult to supply voltage from the second voltage applying means and It is difficult to reach the target potential.

Description of drawings

These and other aspects of the apparatus of the present invention are further described and illustrated with reference to the accompanying drawings, in which:

FIG. 1 is a schematic diagram showing the general structure of an LCD according to an embodiment of the present invention;

Fig. 2 is a sectional view along line II-II of Fig. 1;

Figure 3 is a timing chart for explaining the operation of the LCD shown in Figure 1; and

FIG. 4 is a timing chart for explaining the operation of an LCD according to the prior art.

Description of the optimal solution

FIG. 1 is a schematic diagram showing an LCD according to an embodiment of the present invention. This LCD includes a liquid crystal panel 10 having a pixel array arranged in, for example, an MxN matrix, and a horizontal drive circuit 20 and a vertical drive circuit 30 disposed outside the liquid crystal panel 10 as first and second voltage applying means.

FIG. 2 shows an exemplary cross-sectional structure of the liquid crystal panel 10 . The liquid crystal panel 10 is equipped with a driving substrate 11 on which a plurality of pixel electrodes 13 are formed through an insulating layer 12, and an opposing substrate 16 arranged opposite to the driving substrate 11 with a given distance therebetween, and A common electrode 15 and a color filter (not shown) are provided on the driving substrate surface thereof. The liquid crystal layer 14 is installed between the drive substrate 11 and the opposite substrate 16 . The pixel electrodes 13 are arranged corresponding to respective pixels in a matrix such as MxN and are electrically connected to a drain such as a TFT 17 provided as a switching element formed inside the insulating layer 12 in one-to-one correspondence with the pixel electrodes 13. The TFT 17 may use a so-called top gate type or bottom gate type TFT.

The gate electrodes of the TFT 17 are arranged in a matrix corresponding to the pixel matrix. The pixel electrodes 13 are electrically connected row by row to form a scan line of the first conductive line. The M scanning lines 41-1 to 41-m (FIG. 1) constitute the first wire group. The source electrodes of the TFT 17 are electrically connected column by column to the signal lines constituting the second wires, and the N signal lines 42-1 to 42-n constitute the second wire group.

Here, the horizontal drive circuit 20 is provided on the signal line 42-1 plane of the first column C1. The horizontal driving circuit 20 has a function of selecting a row to be driven, and sequentially applies a scanning voltage called a gate voltage to each scanning line of the group of scanning lines 41-1 to 41-m. More specifically, the horizontal drive circuit 20 sequentially supplies a scan pulse as a scan voltage to each scan line connected to the gate electrodes of the TFTs 17 of the corresponding row in one cycle. One vertical scan period corresponds to one cycle.

Here, the vertical driving circuit 30 is provided on the face of the M-th scanning line 41-m of the screen. This vertical driving circuit 30 has a function of selecting a column to be driven, and receives an image signal S _data from a voltage circuit (not shown) for converting the received image signal S _data to be applied to a corresponding signal line Signal voltages from 42-1 to 42-n.

The LCD is also equipped with a control circuit 50 for changing the time period of applying the signal voltage to the signal lines and applying the gate voltage to the scanning lines within one vertical scanning period during the period when the signal voltages are applied to all the scanning lines. The control circuit 50 of this embodiment controls each horizontal scanning period, so the horizontal scanning from the Mth scanning line 41-m closest to the vertical driving circuit 30 to the first scanning line 41-1 farthest from the vertical driving circuit 30 The cycle gradually increases. The control circuit 50 controls each voltage application period so that the period of time in which the signal voltage is applied to the pixel row via the signal line from the near end face to the far end face is gradually increased. Here, the control circuit 50 corresponds to a specific example of the "period changing means" of the present invention.

The operation of the LCD will be explained with reference to FIG. 3 . The vertical scanning period is denoted by T. FIG. 3 is a timing chart showing timing of voltages applied to pixels in an LCD according to this embodiment.

In the LCD shown in FIG. 3A according to this embodiment, a sequential scanning voltage is applied to the first scanning line 41-1 through the horizontal driving circuit 20 in the horizontal scanning period _t1 , and this sequential scanning voltage is supplied to The gate electrode of the TFT 17 present in the first row of pixels. At this time each TFT 17 of the first row of pixels is turned on and the TFT conducts electricity between its source and drain electrodes. As described above, since the selection period of the first scanning line 41-1 within one vertical scanning period T, that is, the voltage application period, is the longest among the M scanning lines, the horizontal scanning period is at least longer than T/ M long.

After the horizontal scanning period _t1 ends, as shown in _FIG . 3B, the sequential scanning voltage is applied to the second scanning line 41-2 during the horizontal scanning period _t2 shorter than the period t1. Similar to the case of the first scanning line 41-1, this allows the sequential scanning voltage to be supplied to the gate electrodes of the TFTs 17 of the pixels of the second row and the TFTs 17 of the second row to be turned on.

Then, as shown in FIGS. 3C to 3E , since the horizontal scanning period satisfies t ₂ >t ₃ ... >t _m and t ₁ +t ₂ +t _m-1 +t _m =T, the respective sequential scanning voltages also is applied sequentially from the third row 41-3 onwards to the scan line 41-m.

On the other hand, the signal voltage according to the image signal is supplied to the corresponding signal lines 42-1 to 42-n through the vertical driving circuit 30 during one vertical scanning period T. When the TFT 17 is turned on, a signal voltage is supplied to the corresponding pixel electrode 13 through the corresponding TFT 17 at that time. As a result, the signal voltage is applied to those portions of the liquid crystal layer 14 between the common electrode 15 and the pixel electrode 13 to which the signal voltage is applied, so the liquid crystal layer 14 is driven and an image is displayed on the liquid crystal panel.

FIGS. 3F and 3G respectively show exemplary signal voltage waveforms of the nearest end surface NES and the most distal end surface FES of the first signal line 42 - 1 . Here, within a certain vertical scanning period T, the control circuit 50 controls each horizontal scanning period, so the horizontal scanning line from the first scanning line 41-1 farthest from the vertical driving circuit 30 to the Mth scanning line 41-m The scanning period is gradually shortened. The control circuit 50 controls each signal voltage application period by increasing the time period in which the signal voltage is applied from the nearest end surface NES to the most distal end surface FES of the signal lines 42-1 to 42-n. Therefore, the pixels and the like on the first row R1 and the second row R2 are not affected by the time constant of the signal line. Therefore, when a scan line far from the vertical driving circuit 30 is selected, it takes a relatively long time for the signal voltage of the area corresponding to the pixel supplied to the signal line by the vertical driving circuit 30 to reach a target value. However, since a longer horizontal scanning period is set for this scanning line, the target voltage can still be achieved, that is, the signal voltage is written into the pixel electrode 13 with the correct target voltage. This makes it possible to obtain images of excellent quality without brightness deviations, color shifts, flicker or other artifacts. In addition, since the on-state time of the TFTs 17 of the pixels on the far end faces of the signal lines 42-1 to 42-n is longer than those on their near end faces NES, even if the output current capability of the driving circuit It is lower and the time for charging the far end surface FES of the signal line is longer, but the pixel electrode 13 of the pixel on the far end surface FES of the signal line still reaches the corresponding target voltage. Therefore, it is not necessary for the vertical driving circuit 30 to have a large driving capability in this embodiment. Thus, the power required by the vertical drive circuit 30 is lower.

According to the LCD of this embodiment, because the control circuit 50 is adapted to vary each time period of the gate voltage applied to the corresponding scan line within a fixed vertical scan period and to vary the voltage applied to the pixel between the near-end face and the far-end face Therefore, the time period of the voltage applied to the scan line corresponding to the area of the signal line where it takes a relatively long time to supply the signal voltage to the target value can be extended. Therefore, the signal voltage can be written on the pixel electrode 13 with the achieved target voltage, thereby improving the display performance of the device.

In addition, by changing the time period for applying the signal voltage to the pixel so that it is longer at the near end face of the signal line than at the far end face of the signal line, even if the driving ability of the vertical drive circuit 30 is reduced, it is not provided to any pixel electrode. The voltage of 13 still reached the target voltage. This reduces the power consumption of the device.

Although the present invention has been explained with the embodiments thereof, the present invention is not limited to the above-mentioned embodiments, but can be implemented with various modifications. For example, the foregoing embodiment has described the situation that the vertical drive circuit 30 is provided on the Mth scan line 41-m plane of the liquid crystal screen, but the vertical drive circuit 30 may also be provided on the first scan line 41-1 of the liquid crystal screen. superior. In addition, the vertical drive circuit 30 may be provided on the same face of the liquid crystal panel as the horizontal drive circuit 20 to obtain a so-called narrow frame display device.

The above embodiments have described the case without the so-called vertical blanking period, but it is obvious that the effects of the present invention can also be obtained with the vertical blanking period.

The above embodiment has described the case where the control circuit 50 controls each horizontal scanning period to gradually change the horizontal scanning period and the signal voltage application period, but these periods do not always have to be gradually increased and the control circuit 50 may control each signal voltage application period , so the signal voltage application period of the far-end surface away from the vertical drive circuit 30 becomes longer than the signal voltage application period of the near-end surface. Alternatively, the control circuit 50 may control each signal voltage application period so that the horizontal scanning period of a scanning line far from the vertical driving circuit 30 becomes longer than that of a scanning line close to the vertical driving circuit 30 .

The above embodiments have described the case where the control circuit 50 controls both the horizontal scanning period and the signal voltage application period, but the effect of the present invention can be obtained when the control circuit controls only one of the horizontal scanning period or the signal voltage application period.

The above embodiments have described the case where the scan lines are scanned row by row, but the present invention is also applicable to the case where the scan lines are scanned dot by dot.

In the above-described embodiments, the TFT 17 is used as the switching element, but it is also possible to use other switching elements such as MOSFETs (Metal Oxide Semiconductor Field Effect Transistors). Furthermore, the above-mentioned embodiments have described the case of a so-called active matrix driving type device using switching elements, but the present invention is also applicable to a so-called passive matrix driving type device not using any switching elements.

The above embodiments have described the case where a color filter (not shown) is formed on the counter substrate 16, but it is not necessary to form the color filter.

In addition, the above-mentioned embodiments have described the LCD as an example display device, but the present invention is widely applicable to other display devices in which pixels are arrayed in a matrix. Such display devices include plasma displays, field emission displays, and organic electroluminescence displays.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not limit the claim. The word "comprising" does not exclude other elements or steps than those listed in a claim. The word "a" preceding an element does not exclude the presence of a plurality of such elements. The invention can be implemented by means of hardware comprising several distinct elements, and a suitably programmed computer. In the device claim enumerating several means, some of these means can be provided with one and the same hardware object. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures has no advantages.

Claims (5)

1. A liquid crystal display device, comprising: a matrix of pixel rows and pixel columns; a set of first conductive lines, each first conductive line coupled to each pixel row; a set of second conductive lines, each second conductive line coupled to each pixel column; a first voltage applying device for sequentially applying a scan voltage to each of the first wires; and The second voltage applying device is used to apply signal voltages to each second conductive line in synchronization with the sequential application of the scanning voltage to the first conductive line, and is characterized in that: the display device also includes a pixel row according to a pixel row and a second voltage A period changing device that varies the time period during which a signal voltage is applied by applying the distance between the devices. 2. The liquid crystal display device of claim 1, wherein the period changing means changes the time period of applying the scanning voltage to each of the first wires in synchronization with the time period of applying the signal voltage to each of the second wires. 3. The liquid crystal display device of claim 1, wherein the period varying means selects a longer time period for applying the signal voltage when a signal interval between a pixel row and the second voltage applying means increases. 4. The liquid crystal display device of claim 1, wherein the application of the scanning voltage to all the first wires is completed within a predetermined period of time. 5. A method for driving a liquid crystal display device, said liquid crystal display device comprising: a matrix of pixel rows and pixel columns; a first group of wires, wherein each wire is coupled to a respective pixel row; a second group of wires, wherein each wire is coupled to each pixel column; and a driver stage that drives the second set of wires, Said method comprises the following steps: sequentially applying a scan voltage to each of the first wires; and Applying a signal voltage to each of the second wires synchronously with applying the scanning voltage to the first wire is characterized in that: the time period for applying the scanning signal changes according to the distance between the pixel row to which the scanning voltage signal is applied and the driving stage.

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